IEC 61000-4-5 uses 2 ohms since the current is injected into the shield -- the intent being to see if currents induced into the shield of a cable will cause upsetting surge voltages on the inner conductors. 42 ohms is used for I/O lines where the surge is injected directly on the signal lines --- the added 40 ohms is to limit surge currents into the I/O ports.... Not an issue when the current is on the shield itself. I was convenor of WG 11 that did the revision, but I don't remember exactly why the 10nF capacitor was removed. I do remember there was considerable discussion, but not the details. Might have had something to do with the cable capacitance is the inherent capacitance of the cable and that the additional 10nF was not representative. Perhaps someone else remembers the discussion... Michael Hopkins Thermo Fisher Scientific One Lowell Research Center Lowell, MA 01852 Tel: +1 978 275 0800 ext. 334 Fax: +1 978 275 0850 mobile: +1 603 765 3736 [email protected]
_____ From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Monday, December 17, 2007 11:56 AM To: [email protected] Subject: EN50121-4: surges on shielded lines Dear list members, I'm writing the EMC test spec. for a wayside railway equipment, reference standard is EN50121-4. I've got an interpretation problem on the surge test on I/O shielded cables: it's a balanced RS-485 like communication line, the shield is connected only at the EUT side. Cable lenght may sometimes exceed 30m. EN50121-4 Table 3 (note 3) recommends a generator source impedence of 42 Ohm, both for line-to-line and line-to-gnd test and with no specific reference to shielded lines. But if I look at the test setup according IEC 61000-4-5 par. 7.6 (fig. 17), it requires a generator source impedence of 2 Ohm. Am I right supposing that the specific EN50121-4 standard has anyway priority over the 61000-4-5 and I have to use 42 Ohm ? Moreover, previous version of IEC 61000-4-5 suggested (in the above quoted fig.17) to add a 10nF termination capacitor between shield open end and gnd to simulate cable capacitance, why has it been removed ? Thanks in advance for your precious time Best Regards Francesco Campedelli Product Engineering - HW Design ALSTOM Ferroviaria s.p.a. E-mail: [email protected] :.________________ CONFIDENZIALE: Questo messaggio e gli eventuali allegati sono confidenziali e riservati. Se vi è stato recapitato per errore e non siete fra i destinatari elencati, siete pregati di darne immediatamente avviso al mittente. Le informazioni contenute non devono essere mostrate ad altri, né utilizzate, memorizzate o copiate in qualsiasi forma. CONFIDENTIALITY : This e-mail and any attachments are confidential and may be privileged. If you are not a named recipient, please notify the sender immediately and do not disclose the contents to another person, use it for any purpose or store or copy the information in any medium. - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
